164 
GEOLOGY OF THE THIRD DISTRICT. 
mass at innumerable points. The usual thickness is about fourteen feet; the greatest ob¬ 
served thickness, twenty feet. 
It has not been seen beyond the town of Smyrna in an east direction; but from thence 
west it extends into the fourth district, through Madison, Onondaga and Cayuga. Its locali¬ 
ties are numerous in the last two counties ; but it was not seen in Madison, though it must 
exist there. The Tully limestone makes a good, but not a white lime ; owing, in all proba¬ 
bility, to the presence of carbonates of iron and manganese. These two minerals, as high up 
as the coal deposit, appear to increase from the Hamilton group, as the age of the rock di¬ 
minishes. Minute veins of carbonate of iron are seen in the limestone ; and the fossils of 
the rocks above it are often replaced by the two carbonates, particularly the encrinital stems 
and disks. 
There are two fossils in this rock which are wholly peculiar to it. The first is the Cuboiclal 
atrypa, No. 1 of the wood-cut. This is an English name, given to a fossil by Mr. Phillips, 
which, from the figure and description conjoined, shows identity with that of the Tully lime¬ 
stone. It is placed in the Devonian system, which gives but a feeble light as to the geologi¬ 
cal identity of the strata in which they are found. The precise position which the cuboides 
holds in New-York, will soon determine the position of its kindred one in England. The 
cuboides is found in most of the localities of this rock. 
No. 2. The Tully orthis is the other fossil: It appears also to be an English one, from 
Mr. Conrad’s information, having been described years ago by Martin, under the name of 
Anomia resupinata ; but the former name is preferred, being a sure one. 
No. 3. The Lentiform atrypa (A. lentiformis), from its shape like a lentil or lens, has 
always been considered by Mr. Conrad as the young of the A. prisca. It may be so ; but 
its size is remarkably uniform, both in this rock, and in the corniferous and others. Its 
numbers are great, and show no intermediate sizes, and none of the larger kind are found in 
the Tully limestone ; all which facts indicate a shell that had attained its growth, rather than 
a growing one. It is figured in order to draw attention to it, and from its constant association 
with Nos. 1 and 2. 
There are other fossils in this rock, but they are rare, with the exception of a very small 
orthis at Smith’s ledge, and a Strophomena resembling the linear, which occurs in great abund¬ 
ance in the upper part of the limestone at Tully four-corners. Among the others, are the 
Calymene marginalis, the Avicula reticulata, and the Atrypa didyrna. Both of the latter are 
also European fossils, which I have not yet seen. By their means, Mr. Conrad believes that 
he has shown the identity of the Tully limestone with the Aymestry limestone of Mr. Mur¬ 
chison. 
Localities where observed. The first point going west, is on the turnpike from Sherburne 
to De Ruyter, about eight miles from the former village. It appears in a low side-hill, forming 
the bank of the creek where the road crosses it. About four layers are exposed, ranging by 
the side of the creek. It is more impure there than farther west. 
In Madison county it was not seen, but it must exist there, as it is found to the northwest 
of De Ruyter village, about two miles distant. It appears in the hill-side more than one 
